With the progress of small-size, high-speed and lightweight electronic devices such as cellular phones and personal computers, the capacitor used for these electronic devices is demanded to be smaller in size and lighter in weight and to have a larger capacitance and a lower equivalent series resistance (ESR).
As an example of such a capacitor, an electrolytic capacitor has been proposed, which capacitor is produced by anodically oxidizing a sintered body (anode body) obtained by sintering valve-acting metal powder such as tantalum which can be anodized to form a dielectric layer made of the oxide of the metal on the surface of the sintered body.
The electrolytic capacitor using tungsten as a valve-acting metal and employing a sintered body of the tungsten powder as an anode body can attain a larger capacitance compared to the electrolytic capacitor obtained with the same formation voltage by employing an anode body of the same volume using the tantalum powder having the same particle diameter.
The present inventors proposed a tungsten powder comprising tungsten silicide in the particle surface region and having a silicon content of 0.05 to 7 mass %; an anode body comprising the sintered body of the tungsten powder; an electrolytic capacitor; and a production method thereof (Patent Document 1; WO 2012/086272; US 2013/277626 A1).